Generic Function Find-Item (12 methods)

Part of:

Find item in container using the container's test method for comparisons. The test method must take two parameters. The first will be the item being searched for; the second will be an item in the container. If the container has a key (keyed-container-mixin), then the test is performed on the item and the key of each element in the container. Find-item returns nil if the item is not found and it returns the element in the container if it is.